Subject: Re: Re: bug#16830: [Bug] 24.3.50; massive slow down in forward-line

From: Dmitry Antipov <[email-masked]>
Date: Mon, 17 Mar 2014 19:05:27 +0400

On 03/10/2014 10:58 PM, Eli Zaretskii wrote:

> It would be nice to be able to turn the cache on and off dynamically,
> depending on the actual line length of the buffer.  I tried to
> implement this, but my naive implementation didn't work well, because
> sampling of the lines tends to be extremely un-representative.  If
> someone can come up with a smarter implementation, please show it.

What if we just maintain the '\n' counter per each buffer text?
With that, finding an average line length is straightforward,
and the very basic implementation looks fairly simple; this
should be helpful in maintaining newline_cache as well.

Dmitry

=== modified file 'src/buffer.c'
--- src/buffer.c	2014-03-15 11:16:12 +0000
+++ src/buffer.c	2014-03-17 14:42:01 +0000
@@ -573,6 +573,7 @@
   BUF_END_UNCHANGED (b) = 0;
   BUF_BEG_UNCHANGED (b) = 0;
   *(BUF_GPT_ADDR (b)) = *(BUF_Z_ADDR (b)) = 0; /* Put an anchor '\0'.  */
+  BUF_NL (b) = 0;
   b->text->inhibit_shrinking = false;
   b->text->redisplay = false;

=== modified file 'src/buffer.h'
--- src/buffer.h	2014-01-01 07:43:34 +0000
+++ src/buffer.h	2014-03-17 14:42:01 +0000
@@ -91,6 +91,9 @@
 /* Modification count as of last visit or save.  */
 #define SAVE_MODIFF (current_buffer->text->save_modiff)
 
+/* How many '\n' in the buffer.  */
+#define NL (current_buffer->text->nl)
+
 /* BUFFER_CEILING_OF (resp. BUFFER_FLOOR_OF), when applied to n, return
    the max (resp. min) p such that
 
@@ -183,6 +186,9 @@
 /* FIXME: should we move this into ->text->auto_save_modiff?  */
 #define BUF_AUTOSAVE_MODIFF(buf) ((buf)->auto_save_modified)
 
+/* How many '\n' in the buffer.  */
+#define BUF_NL(buf) ((buf)->text->nl)
+
 /* Compaction count.  */
 #define BUF_COMPACT(buf) ((buf)->text->compact)
 
@@ -463,6 +469,9 @@
     /* Properties of this buffer's text.  */
     INTERVAL intervals;
 
+    /* How many '\n' in this buffer's text.  */
+    ptrdiff_t nl;
+
     /* The markers that refer to this buffer.
        This is actually a single marker ---
        successive elements in its marker `chain'

=== modified file 'src/insdel.c'
--- src/insdel.c	2014-01-01 17:44:48 +0000
+++ src/insdel.c	2014-03-17 14:55:57 +0000
@@ -560,7 +560,20 @@
       return to_addr - initial_to_addr;
     }
 }
-
+
+/* Count '\n' in [PTR..PTR + NBYTES).  */
+
+static ptrdiff_t
+count_newlines (const char *ptr, ptrdiff_t nbytes)
+{
+  const char *p = ptr;
+  ptrdiff_t count = 0, restbytes = nbytes;
+
+  while (restbytes > 0 && (p = memchr (p, '\n', restbytes)))
+    p++, count++, restbytes = nbytes - (p - ptr);
+  return count;
+}
+
 /* Insert a string of specified length before point.
    This function judges multibyteness based on
    enable_multibyte_characters in the current buffer;
@@ -814,6 +827,9 @@
   MODIFF++;
   CHARS_MODIFF = MODIFF;
 
+  /* Count newlines in new text.  */
+  NL += count_newlines (string, nbytes);
+
   memcpy (GPT_ADDR, string, nbytes);
 
   GAP_SIZE -= nbytes;
@@ -924,6 +940,9 @@
     make_gap (outgoing_nbytes - GAP_SIZE);
   UNGCPRO;
 
+  /* Count newlines in string text.  */
+  NL += count_newlines (SSDATA (string) + pos_byte, nbytes);
+
   /* Copy the string text into the buffer, perhaps converting
      between single-byte and multibyte.  */
   copy_text (SDATA (string) + pos_byte, GPT_ADDR, nbytes,
@@ -1001,6 +1020,11 @@
   record_insert (GPT, nchars);
   MODIFF++;
 
+  /* Add newlines from new text.  */
+  NL += count_newlines (text_at_gap_tail
+			? (char *) GAP_END_ADDR - nbytes
+			: (char *) GPT_ADDR, nbytes);
+
   GAP_SIZE -= nbytes;
   if (! text_at_gap_tail)
     {
@@ -1138,6 +1162,9 @@
     emacs_abort ();
 #endif
 
+  /* Add newlines from gap.  */
+  NL += count_newlines ((char *) GPT_ADDR, outgoing_nbytes);
+
   record_insert (PT, nchars);
   MODIFF++;
   CHARS_MODIFF = MODIFF;
@@ -1340,6 +1367,9 @@
      combining.  */
   if (! EQ (BVAR (current_buffer, undo_list), Qt))
     deletion = make_buffer_string_both (from, from_byte, to, to_byte, 1);
+  
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
 
   GAP_SIZE += nbytes_del;
   ZV -= nchars_del;
@@ -1360,6 +1390,9 @@
   if (GAP_SIZE < outgoing_insbytes)
     make_gap (outgoing_insbytes - GAP_SIZE);
 
+  /* Add newlines from string text.  */
+  NL += count_newlines (SSDATA (new), insbytes);
+
   /* Copy the string text into the buffer, perhaps converting
      between single-byte and multibyte.  */
   copy_text (SDATA (new), GPT_ADDR, insbytes,
@@ -1470,6 +1503,9 @@
   if (to < GPT)
     gap_left (to, to_byte, 0);
 
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
+
   GAP_SIZE += nbytes_del;
   ZV -= nchars_del;
   Z -= nchars_del;
@@ -1489,6 +1525,9 @@
   if (GAP_SIZE < insbytes)
     make_gap (insbytes - GAP_SIZE);
 
+  /* Add newlines from replacement text.  */
+  NL += count_newlines (ins, insbytes);
+
   /* Copy the replacement text into the buffer.  */
   memcpy (GPT_ADDR, ins, insbytes);
 
@@ -1737,6 +1776,9 @@
      adjusting the markers that bound the overlays.  */
   adjust_overlays_for_delete (from, nchars_del);
 
+  /* Do not count newlines from deleted text any more.  */
+  NL -= count_newlines ((char *) BYTE_POS_ADDR (from_byte), nbytes_del);
+
   GAP_SIZE += nbytes_del;
   ZV_BYTE -= nbytes_del;
   Z_BYTE -= nbytes_del;